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Abstract

We have developed a technique for the accurate and precise determination of 34S/32S isotope
ratios (δ34S) in sulfur-bearing minerals using solution and laser ablation multiple-collector
inductively coupled plasma mass spectrometry (MC-ICP-MS). We have examined and
determined rigorous corrections for analytical difficulties such as instrumental mass bias,
unresolved isobaric interferences, blanks, and laser ablation- and matrix-induced isotopic
fractionation. Use of high resolution sector-field mass spectrometry removes major isobaric
interferences from O2+. Standard–sample bracketing is used to correct for the instrumental mass
bias of unknown samples. Blanks on sulfur masses arising from memory effects and residual
oxygen-tailing are typically minor (< 0.2‰, within analytical error), and are mathematically
removed by on-peak zero subtraction and by bracketing of samples with standards determined at
the same signal intensity (within 20%). Matrix effects are significant (up to 0.7‰) for matrix
compositions relevant to many natural sulfur-bearing minerals. For solution analysis, sulfur
isotope compositions are best determined using purified (matrix-clean) sulfur standards and
sample solutions using the chemical purification protocol we present. For in situ analysis, where
the complex matrix cannot be removed prior to analysis, appropriately matrix-matching
standards and samples removes matrix artifacts and yields sulfur isotope ratios consistent with
conventional techniques using matrix-clean analytes. Our method enables solid samples to be
calibrated against aqueous standards; a consideration that is important when certified,
isotopically-homogeneous and appropriately matrix-matched solid standards do not exist.
Further, bulk and in situ analyses can be performed interchangeably in a single analytical session
because the instrumental setup is identical for both. We validated the robustness of our analytical
method through multiple isotope analyses of a range of reference materials and have compared
these with isotope ratios determined using independent techniques. Long-term reproducibility of
S isotope compositions is typically 0.20‰ and 0.45‰ (2σ) for solution and laser analysis,
respectively. Our method affords the opportunity to make accurate and relatively precise S
isotope measurement for a wide range of sulfur-bearing materials, and is particularly appropriate
for geologic samples with complex matrix and for which high-resolution in situ analysis is
critical.

We present 28 multiple sulfur isotope measurements of seawater sulfate (δ34SSO4δ34SSO4 and Δ33SSO4Δ33SSO4) from the modern ocean over a range of water depths and sites along the eastern margin of the Pacific Ocean. The ...

The subsurface biosphere in the basaltic ocean crust is potentially of major
importance in affecting chemical exchange between the ocean and lithosphere. Alteration
of the oceanic crust commonly yields secondary pyrite ...

Glasses produced from decompression experiments conducted by Fiege et al. (2014a) were used to
investigate the fractionation of sulfur isotopes between fluid and andesitic melt upon magma
degassing. Starting materials ...

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